Synthetic Metals (v.157, #21)

The mechanism of the intramolecular diamagnetic ring currents in the (4n  + 2)π electronic states of neutral acenes with microscopic sizes such as naphthalene (10ac), anthracene (14ac), and tetracene (18ac) is discussed, and compared with that of electrical conductivity in normal metals and conventional superconductors with macroscopic sizes. Diamagnetic intramolecular ring current in the (4n  + 2)π electronic states of neutral acenes with microscopic sizes can be explained in terms of the electron pairing caused by attractive Coulomb interactions between two electrons with opposite spins occupying the same nondegenerate π molecular orbitals. The critical temperature T c neutral acenes at which diamagnetic intramolecular ring current states are destroyed for the (4n  + 2)π electronic states of each neutral acene with microscopic sizes such as 10ac, 14ac, and 18ac are estimated to be much larger than the critical temperature (T c,BCS) for the conventional superconductors with macroscopic sizes. Energy lowering in the exponential factor in the equation for T c,BCS, originating from continuous energy levels of electronic states in the conventional superconductors with macroscopic sizes, and the energy lowering factor which is proportional to the T c neutral acenes values, originating from discrete energy levels of electronic states in acene molecules with small sizes such as 10ac, 14ac, and 18ac, are the main reason that the T c neutral acenes values for the (4n  + 2)π electronic states of neutral acenes with microscopic sizes are estimated to be much larger than the T c,BCS values for the conventional superconductors with macroscopic sizes. In bulk system, electrical conductivity in the (4n  + 1)π electronic states of the monocation crystal is compared with that in the (4n  + 2)π electronic states of neutral acene crystals formed by small acene molecules.
Keywords: Diamagnetic intramolecular ring current; Resonance energies; (4n  + 2)π-electronic systems; Microscopic sized acene molecule; Electron pairing;

EPR, dc and ac magnetic measurements on lightly doped poly(3-dodecylthiophene) with FeCl3 are reported. The zero-field-cooled and field-cooled curves obtained by a SQUID magnetometer confirmed magnetic hysteresis, beginning close to the room temperature. Magnetic hysteresis is close-knit with structural irreversibility of polymeric chains. Structural irreversibility induces changes in proportions of diamagnetic, Pauli, Currie, and polaron magnetic contributions of the polymeric system.
Keywords: Polyalkylthiophenes; Conducting polymers; Magnetism; Polarons;

Synthesis and characterization of red phosphorescent-conjugated polymers containing charged iridium complexes and carbazole unit by Yun Deng; Shu-Juan Liu; Qu-Li Fan; Chun Fang; Rui Zhu; Kan-Yi Pu; Li-Hui Yuwen; Lian-Hui Wang; Wei Huang (813-822).
A series of homogeneous red-light phosphorescent polymers with charged iridium (Ir) complex in the backbones and carbazole unit on the side were synthesized by Suzuki polycondensation. These polymers are made up of three repeat units: (i) charged iridium (Ir) complex; (ii) 9,9-dihexylfluorene; (iii) 9,9-bis(N-carbazolyl-hexanyl)-fluorene. Their structures have been identified by nuclear magnetic resonance (NMR) and elemental analysis. All chelating polymers displayed good thermal stability, redox reversibility and film formation. Compared with our former study on these charged Ir complex containing polymers, the addition of carbazole unit has a strong influence on their hole injection and charge attraction ability as well as the host–guest energy transfer efficiency.
Keywords: Carbazole; Hole injection; Energy transfer; Iridium complex; Polymers; Red-phosphorescence;

We, in this study, focus on the effect of sulfonated poly(styrene-ethylene-butylene-styene) (SSEBS) as a binder to enhance electrochemical property of poly(3-methyl thiophene) (P3MT) as a active material of cathode in redox system. P3MT was polymerized using FeCl3 as both a dopant and an initiator. The cathode was prepared to cast on Al mesh the slurry mixed P3MT, carbon black and binder (8:1:1 wt.%). The specific discharge capacity of P3MT–SSEBS electrode is high as 80 mAh/g, while that of P3MT–SEBS and P3MT–PVDF electrodes have lower values as 50 and 25 mAh/g, respectively. The reason for this is that SSEBS acts as a binder as well as a dopant. In an advance, the effect of sulfonation promotes the miscibility, contact area and affinity.
Keywords: Poly(3-methyl thiophene); Poly(styrene-ethylene-butylene-styene); Sulfonation; Polymer battery; Binder;

α-Quaterthiophene–polyethylene blends: Phase behaviour and electronic properties by Pascal Wolfer; Christian Müller; Paul Smith; Mohammed A. Baklar; Natalie Stingelin-Stutzmann (827-833).
We demonstrate that blending α-quaterthiophene (4T) with high-density polyethylene (HDPE) under judiciously chosen processing conditions allows preparation of continuous thin films of insulator content as high as 90 wt% without considerably sacrificing the electronic properties of the semiconducting species, as measured in field-effect transistors (FETs). Similar behaviour was recently reported for all-polymeric crystalline–crystalline semiconducting blends such as poly(3-hexylthiophene):HDPE. However, while that previous work focussed on the sequence in which the two components crystallize, we show here that for the present small molecule:polymer binaries – in addition to the crystallization sequence – the extent of solid–solid phase separation that occurs during blend preparation strongly affects the electronic properties of the active layers.
Keywords: α-Quaterthiophene; Blends; Field-effect transistor (FET);

Fluorescence study of intrachain and interchain ultrafast processes in domain-structured polythiophene by Ignác Bugár; Michal Žitnan; Dušan Velič; Gabriel Čík; Dušan Chorvát (834-840).
Exciton dynamics of poly(3-dodecylthiophene) were studied by steady state and femtosecond time-resolved fluorescence spectroscopy. Comparing the solution and solid-state results intrachain and interchain exciton transfer processes were distinguished. The steady-state spectra revealed extra nonradiative relaxation channel in solid state and excitation wavelength-dependent fluorescence, suggesting non-trivial energy level structure. According to the observed wavelength dependent spectral splitting phenomena a domain model of the poly(3-dodecylthiophene) solid structure were suggested. The time-resolved results confirmed the domain concept unveiling two spectral areas with different fluorescence character. Moreover, the time-resolved study was able to differentiate between two poly(3-dodecylthiophene) samples with small change (13%) of their regioregularity. The obtained results are a demonstration of usefulness of fluorescence spectroscopy to analyze the interchain polymer structure in solid state.
Keywords: Polyalkylthiophenes; Femtosecond spectroscopy; Fluorescence; Exciton dynamics; Interchain ordering; OLED;

Wide band gap cross-linkable semiconducting polymer LED by Olga Solomeshch; Young-Jun Yu; Vladislav Medvedev; Alexey Razin; Batya Blumer-Ganon; Yoav Eichen; Jung-Il Jin; Nir Tessler (841-845).
A new derivative (PVK-Ox) of poly(vinyl carbazole) (PVK) was prepared by tethering oxetane pendants to the carbazole group through the decamethylene spacer. Photo-patternability of this new PVK-based polymer was investigated through photo-crosslinking reaction under UV light illumination (λ  = 312 nm). We show that the chemical modifications as well as the cross-linking reaction do not degrade the optoelectronic performance of the starting polymer. The potential use of wide band gap cross-linkable polymers as electron-blocking layer is demonstrated. The results indicate that photolithography based on photo-crosslinking is a viable device fabrication tool for organic electronics.
Keywords: Poly(vinyl carbazole); Crosslink; LED; Polymer; Photolithography;

Polyaniline-related ion-barrier anticorrosion coatings by Jianguo Wang; Charlie C. Torardi; Michael W. Duch (846-850).
Ionic permeabilities of coating films were studied with a variety of experimental methods including measurements of membrane potential, salt diffusion, and electron spectroscopy for chemical analysis (ESCA). The results show that polyaniline (PAn) allows diffusion of anions (if PAn is dispersed in a cationic polymer matrix, the resulting film may have cationic defects that allow the passage of cations), a cationic film is permeable to cations, and the combination of a PAn containing primer with the cationic topcoat is an ion-barrier which delays penetration of both anions and cations.
Keywords: Polyaniline; Ion-barrier; Conducting polymers; Membrane potential; Ion permeability;

Polyaniline-related ion-barrier anticorrosion coatings by Jianguo Wang; Charlie C. Torardi; Michael W. Duch (851-858).
A polyaniline (PAn) containing coating layer leads to substrate corrosion in an environment of aggressive anions. A cationic coating results in delamination or blistering. A bipolar coating consisting of a PAn primer and a cationic topcoat inhibits both corrosion and delamination.
Keywords: Polyaniline; Anticorrosion; Ion-barrier coating; Cathodic delamination;

An inorganic–organic photovoltaic device with a structure of [6,6]-phenyl C61-butyric acid methyl ester and p-Si has been fabricated. The ideality factor value of the diode was found to be 2.12. This n value of the diode implies a deviation from ideal junction behavior. The p-Si/PCBM diode shows a photovoltaic behaviour with a maximum open circuit voltage V oc of 0.12 V, and short-circuit current I sc of 0.10 μA under 6 mW/cm2 light illumination. The parasitic resistances for the diode, which are series R S and shunt R sh resistances were calculated to be 5.24 × 104  Ω and 1.95 × 107  Ω, respectively. The capacitance–voltage plot indicates a non-linear behavior, suggesting a non-uniform dopant density profile and interface irregularities of p-Si/PCBM device. The barrier height ϕ b value for the diode was found to be 0.79 eV. It is evaluated that the p-Si/PCBM diode is a photodiode with calculated electronic parameters.
Keywords: p–n heterojunction; Photodiode; Organic semiconductor;

Deep blue electroluminescent phenylene-based polymers by Szu-Po Huang; Guo-Sheng Huang; Show-An Chen (863-871).
We synthesize a series of soluble phenylene-based electroluminescent (EL) polymers with deep blue emission by incorporations of dialkoxy groups (DRO-PPP) and alkoxy-phenyl group (EHB-PPP) on side chains as well as carbazole unit on main chain (EHB-PPP-Cz) using the Yamamoto coupling approach. The latter two modifications (EHB-PPP and EHB-PPP-Cz) lead to blue-shifts in absorption and emission maxima relative to DRO-PPP. In addition, the incorporation of carbazole as co-repeat-unit (EHB-PPP-Cz) leads to a raise of ionization potential (IP) to the level very close to that of the anode, PEDOT:PSS, to facilitate the hole injection. The maximum efficiency of the ITO/PEDOT:PSS/EHB-PPP-Cz/TPBI/CsF/Ca/Al device is 1.12 cd/A with a stable deep blue EL with CIE (0.16, 0.05).
Keywords: Poly(para-phenylene)s; Carbazole; Conjugated polymers; Light emitting diode; Deep blue emission;

A study of the effects metal residues in poly(9,9-dioctylfluorene) have on field-effect transistor device characteristics by Prashant Sonar; Andrew C. Grimsdale; Martin Heeney; Maxim Shkunov; Iain McCulloch; Klaus Müllen (872-875).
The amount of metal residues from organometallic reagents used in preparation of poly(9,9-dioctylfluorene) by palladium catalysed Suzuki and nickel-induced Yamamoto polycondensations have been determined, and their effect upon the behaviour of the polymer in field-effect transistors (FETs) has been measured. The metal levels from material polymerised by Suzuki method were found to be much higher than from that made by the Yamamoto procedure. Simple treatment of the polymers with suitable metal trapping reagents lowered the metal levels significantly, with EDTA giving best results for nickel and triphenylphosphine for palladium. Comparison of the behaviour of FETs using polyfluorenes with varying levels of metal contamination, showed that the metal residues have little effect upon the mobility values, but often affect the degree of hysteresis, possibly acting as charge traps. Satisfactory device performances were obtained from polymer with palladium levels of 2000 μg/g suggesting that complete removal of metal residues may not be necessary for satisfactory device performance.
Keywords: Conjugated polymer; Field-effect transistor; Organometallic coupling; Charge carrier mobility; Charge trapping;

Structure, surface topography and electrochemical properties of cast films formed by fullerenes and their compositions with salt matrices by N.F. Goldshleger; V.I. Zolotarevsky; A.M. Kolesnikova; E.V. Ovsyannikova; N.M. Alpatova (876-883).
Some properties of films based on fullerene and pyridyl substituted fullerenopyrrolidines were studied. Both direct casting and immobilizing electroactive substances in the tetraoctylammonium bromide (TOAB) or tetraphenylphosphonium bromide matrices were used for modification of the ITO electrode surface. In accordance with X-ray diffraction, pyridyl substituted fullerenopyrrolidines are amorphous, and the lamellar structure of TOAB is retained when fullerene is present in the film. The differences, which are observed in the absorption spectra of the cast coatings of the individual fullerenes or fullerenes in the TOAB matrix as compared with solution spectra testify to the electronic interaction between fullerene molecules in a solid phase. At that, the quaternary ammonium salt participates immediately in the coating self-organization. Atomic force microscopy showed that both the solution composition and addends in the C60 molecules influence the film morphology. Disintegration of fullerenes in the TOAB matrix and their interaction with hydrocarbon chains of TOAB provide the hydrophobic surrounding required for reversible electrochemical reduction of fullerene on an electrode in an aqueous solution. The differences observed for C60 embedded in the tetraphenylphosphonium bromide and TOAB films accentuate the role of a layered structure of the matrix for the reversible electrochemical behavior of fullerene in aqueous solution.
Keywords: [60]Fullerene; Pyridyl substituted fullerenopyrrolidines; Tetraoctylammonium bromide; Coating; Self-organization; Absorption spectra; Cyclic voltammetry; Atomic force microscopy;